1. Field of the Invention
The present invention relates to a servo mark detection device and a servo mark detection method for detecting servo marks recorded on a storage medium such as, for example, a magnetic disk or the like by the use of servo gates, and more particularly, it relates to a servo mark detection device and a servo mark detection method for detecting servo marks recorded on a storage medium by adjusting the phases of servo gates through positional information of the servo marks.
2. Description of the Related Art
In the past, the processing of recording servo information on a storage medium such as a magnetic disk or the like has been performed by using heads built in a magnetic disk drive unit after the storage medium had been assembled into the magnetic disk drive unit. Thus, the servo information, when read and written by the heads, is the information written concentrically with the same axis of rotation, and hence there will be no misalignment or dislocation of the servo information at the times of being written and read, with the intervals between the servo marks recorded on the storage medium being kept substantially constant.
FIG. 9 illustrates the known relation of servo marks (FSMD), servo gates (SG) and servo mark detection windows (SMWin) on the same track used in an ASIC (Application Specific IC). As shown in this figure, the servo marks are read by the read heads and input to the ASIC at constant intervals (a) after a servo mark detection device is turned on. Also, the ASIC generates respective output signals such as a servo gate signal output to an RDC (Read Channel), a servo mark detection window signal used in the ASIC, etc., at constant intervals.
The ASIC asserts the servo gate signal and the servo mark detection window signal based on the values which are set to registers in the ASIC. When a servo mark is detected, it is determined whether the position of the detected servo mark is within a servo area, and when the answer to this question is positive, cylinder information, burst information and the like are read by a read head, whereby the read head is able to recognize the position of the head (cylinder) itself and perform a following or tracking operation. Moreover, when the zone on the storage medium changes in accordance with the movement of the head seeking a target cylinder, the firmware in the magnetic disk drive unit resets the output timing of the respective signals by rewriting the register values of the ASIC according to the intervals of the servo marks in that zone.
On the other hand, in recent years, disk drive units of the kind having a reduced number of storage mediums per unit (e.g., 1 platter, or 2 platters per unit) are becoming mainstreams owing to increased recording densities of the storage mediums and reduction in production costs, and hence the process of writing servo information unit by unit becomes inefficient from a viewpoint of the production time and cost. As a result, there comes to be adopted a method (called a single-disk servo track writing (STW) mode) of recording servo information on several storage mediums in a lump at one time and then assembling the storage mediums thus recorded into respective drive units.
If, however, the single-disk STW mode not used in the past is employed in this manner, there might be caused decentering or eccentricity of the storage mediums from their axis of rotation or an inclination to a device reference surface (e.g., the horizontal plane) in the assembling processes of disk drive units. In this case, servo marks are not input to the ASIC at constant intervals as in the past, thus resulting in a problem that the servo marks cannot be accurately detected by means of known circuit configurations.
FIG. 10 illustrates the relation of servo marks, servo gates and servo mark detection windows in the case where a storage medium, having been produced by the use of the single-disk STW mode, is decentered or offset from its axis of rotation. As shown in this figure, the intervals between the servo marks are (a+b), (a+c), etc., due to the eccentricity of the storage medium, where a, b and c are all assumed to be certain constants, with their relations being a greater than b, a greater than c, and bxe2x89xa0c. Thus, the servo mark intervals are not constant or equal to (a). In this case, if a servo mark (50) is located outside or radially outward of a corresponding servo gate (and/or a corresponding servo mark detection window), there will be misdetection of the servo mark (50).
In the case of the known ASIC""s configuration, it is necessary to reset the on/off timing of the servo gates and the servo mark detection windows in order to prevent the dropped servo marks by such a cause. However, when the method of resetting the values of the registers for the servo gates and servo mark detection windows by means of the firmware is adopted, there will arise another problem in that the access time is increased, resulting in an accordingly increased overhead of the firmware.
In addition, the storage medium usually has recording surfaces on the opposite sides thereof, and when the heads are changed over for reading information from one to the other recording surface, a time gap or interval might be caused due to such a head change-over operation, thus giving rise to a further problem of misalignment or dislocation. FIG. 11 illustrates one example of misalignment or dislocation which would take place when a change is made from one head 0 (e.g., one or front surface) into another head 1 (e.g., the other or back surface). As depicted in this figure, servo marks on the back surface of a storage medium cannot be detected due to misalignments or dislocations (60) of those servo marks relative to the servo gates and/or servo mark detection windows occurring upon changing of the heads. In recent years, increasing densities of storage mediums do not permit such misalignments or dislocations to be disregarded. Accordingly, it is necessary to properly correct the misalignments or dislocations in order to make the effective use of storage mediums.
The present invention has been made in view of the above-mentioned circumstances, and has for its object to provide a servo mark detection device and a servo mark detection method which can detect servo marks on a storage medium without fail by shifting the output timing of servo gates based on preset correction values thereby to correct misalignments or dislocations of servo gates occurring when the storage medium is decentered or offset from its center of rotation or when heads are changed from one to another.
In order to obviate the problems referred to above, according to the present invention, there is provided a servo mark detection device which records in advance information related to positions of servo marks (e.g., correction values such as amounts of position adjustments for correcting misalignments or dislocations of servo marks due to decentering or eccentricity of a storage medium on which the servo marks are recorded) on a storage medium at the time of manufacture thereof. When servo information is read, correction values are also read from the storage medium, so that servo gates are formed based on the correction values thus read. Specifically, timing of the servo gates is usually measured by means of an ASIC by comparing the values set in an internal counter and registers, so that a servo gate signal is turned on and off according to the timing thus set. However, the phases of the servo gates are adjusted by moving or shifting the on/off timing of the servo gate signal according to the correction values thus read. For instance, the amount of displacement (amount of phase) of each servo mark from their intended or reference position, for example represented at b or c in FIG. 10, is collected for each servo mark interval and recorded on the storage medium.
For instance, the on/off timing of the servo gate signal can be shifted by a method of temporarily stopping the internal counter by the correction values or by another method of reloading a certain value into the counter. In this manner, the detection rate of the servo marks can be improved without recreating or resetting the servo gates even if eccentricity is caused in the storage medium upon its mounting on a servo motor. The phases of the servo mark detection windows can be adjusted as in the case of the servo gates. Moreover, the above processing may be controlled by reading the correction values by means of a firmware. Alternatively, control may be carried out in such a manner that hardware internally outputs pulses or the like so as to automatically read correction values.
In addition, misalignment or dislocation of servo marks with respect to servo gates and/or servo mark detection windows upon changing of the heads can be dealt with by storing in advance correction values at the time of changing of the heads in the storage medium and reading the correction values so as to adjust the phases of the servo gates and/or the servo mark detection windows. To this end, correction values for both of the dislocations due to eccentricity and those caused upon changing of the heads are collected and stored in advance, whereby the phases of servo gates can be adjusted by using the eccentricity-based correction values alone before the heads are changed from one to another, alternatively by using both the eccentricity-based correction values and the head-change-based correction values after the changing of the heads, thus making it possible to drastically enhance the servo mark detection ratio.
According to one aspect of the present invention, there is provided a servo mark detection device for forming servo gates to detect servo marks recorded on a storage medium, the device comprising: a reading section for reading information on the positions of the servo marks from the storage medium on which the information on the positions of the servo marks has been recorded in advance; and a servo gate forming section for forming the servo gates based on the information on the positions of the servo marks read by the reading section. In an embodiment of the invention, the servo gate forming section comprises an MPU, registers, a counter, comparators and a firmware. In addition, a timing forming circuit may be employed in place of the firmware.
In a preferred form of the present invention, the information on the positions of the servo marks comprises an amount of displacement of each servo mark with respect to a reference position thereof. The servo gate forming section changes the position of each servo gate to be formed from a servo gate forming position corresponding to the reference position of a corresponding servo mark to a position corresponding to the amount of displacement of the corresponding servo mark.
In another preferred form of the present invention, the amount of displacement of a servo mark to the reference position thereof includes at least one of an amount of misalignment of the servo mark due to an eccentricity of the storage medium occurring upon assembling the storage medium into a disk drive unit, and an amount of misalignment of the servo mark occurring when read/write heads for the storage medium are changed from one to another.
In a further preferred form of the present invention, the servo gate forming section comprises: a counting section for outputting servo gate formation timing when counting a predetermined number of clocks; and a count control section for controlling a counting operation of the counting section based on the information on the positions of the servo marks.
In a yet further preferred form of the present invention, the counting section comprises: a counter for counting the predetermined number of clocks; a count value setting section for setting the predetermined number of clocks to be counted by the counter; and a comparator for comparing a count value of the counter with the predetermined number of clocks set by the count value setting section thereby to output a servo gate forming timing.
In a still further preferred form of the present invention, the count control section controls the counting section in such a manner that the counter of the counting section is stopped or incremented based on the information on the positions of the servo marks.
In a further preferred form of the present invention, the servo mark detection device further comprises a storage section for storing, for a predetermined number of servo marks, the information on the positions of the servo marks recorded on the storage medium. The reading section stores in the storage section the information on the positions of the predetermined number of servo marks read from the storage medium, and the servo gate forming section forms the servo gates based on the information on the positions of the predetermined number of servo marks stored in the storing section. In an embodiment of the invention, the storage section corresponds to a buffer, and the reading section corresponds to a head.
According to another aspect of the present invention, there is provided a servo mark detection method for forming servo gates to detect servo marks recorded on a storage medium, the method comprising: a first step of reading information on the positions of the servo marks from the storage medium in which the information on the positions of the servo marks is recorded in advance; and a second step of forming the servo gates based on the information on the positions of the servo marks read by the reading step.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.